On June 30, 2006, Denis was traded to the Tampa Bay Lightning for Fredrik Modin and Fredrik Norrena. In the 2007–08 season, on December 28, due to his sub-par and inconsistent play, the Lightning waived Denis. After he cleared waivers, Denis was sent down to the Lightning's AHL affiliate, the Norfolk Admirals. The Lightning later recalled Denis from Norfolk on March 26, 2008. Denis replaced goalie Jonathan Boutin, who was earlier recalled from the Admirals on an emergency basis because starting goalie Mike Smith had a sprained left ankle. After the season, Denis was bought out from the Lightning on June 25, 2008.

Denis, who therefore became a free agent, then signed a contract with his hometown team, the Montreal Canadiens, on July 3, 2008.[2] After training camp, Marc Denis was assigned to Montreal's AHL affiliate, the Hamilton Bulldogs. Denis was recalled as an injury replacement for the Canadiens throughout the season and appeared in one game with the Canadiens when he relieved Jaroslav Halak for the third period in a 4–1 loss to the New Jersey Devils on January 2, 2009.[3]